Machine for making blue prints and other photoprints



H. J. BRUNK May 12, 1931.

MACHINE FOR MAKING BLUE PRINTS AND OTHER PHOTOP RINTS Filed Feb. 18. 1928 1 m a. v a 5 A 9 v 0 9 1 2 j 2 E 4 Patented May 12, 1931 UNITED STATES PATENT OFFICE HAROLD J. BRUNK, OF CHICAGO, ILLINOIS, ASSIGNOR TO C. I. PEASE COMPANY, OF CHICAGO, ILLINOIS, A CORPORATION OF DELAWARE MACHINE FOR MAKING BLUE PRINTS AND OTHER PHOTOPRINTS Application filed February 18, 1928.

My invention relates to improvements in machines for making blue prints and other photo prints, and more particularly to the means for holding the sensitized paper and negatives in close contact as they are drawn past the source of light during the printing operation, to insure clear, sharp lines in the finished prints.

Blue printing machines of a type commonly used at the present time are equipped with a curved piece of glass, over which an endless belt passes in contact with the same, the sensitized paper and negatives passing between the belt and the glass, with a source of light such as a row of arc lights on what may be termed the inside of said curved glass. In such machines the sensitized paper is drawn over the glass in a long, wide sheet supplied from a roll so that the printing is practically continuous. In another type of machine a source of light is located within a rotatable glass cylinder around which the sensitized paper is carried, being held upon the cylinder by tapes or belts. In both cases considerable difliculty arises from the fact that neither a curved sheet of glass nor a glass cylinder can be manufactured at the present time with any degree of accuracy. The glass cannot be molded or blown without slight projections or depressions in the surface thereof, and it is almost impossible to subject these glass structures to a grinding operation to render their surface true because of the special machinery that would be required and the high cost of the finished article, which would make its use prohibitive. Photo prints made on both types of machines referred to are, therefore, imperfect in that the sensitized paper is not held in equally close contact with the negatives at all points as the two are travelling over the glass surface, and thus the resulting prints are not sharp and uniform throughout.

It is an object of this invention to overcome these difficulties by providing an improved printer in which the sensitized paper is drawn over a piece of commercial plate glass which is flat and which can be very readily obtained on the market. It is possible to select plate glass which has a perfectly true flat surface and which can be pol- Serial No. 255,481.

ished to a high degree, thus enabling the sensitized paper and tracings to be held in close contact and to slide past the glass readily without danger of sticking.

Another object is to provide improved means for yieldingly pressing the paper against the glass so that the tracings or negatives which are inserted between the two will be held in such intimate engagement with the paper as to produce uniform prints of the highest grade.

Other objects and advantages will be apparent from the following description of one embodiment of the invention.

In the drawing:

The single figure is a sectional elevation of a printing device in which the yielding pres sure is maintained by compressed air.

Referring to the drawing, the frame of the machine 10 supports the various parts ineluding a frame 11 fora sheet of plate glass 12 having a flat, true surface on one side at least. An endless belt 13 passes over rollers 1414 and over additional rollers (not shown), one or more of which drives the belt, causing it to slide upwardly over the surface of the plate glass.

Said belt is yieldingly held against said plate glass by a smoothly finished rigid metal plate 15, made of cast iron, for example. The sensitized paper 16, usually in a sheet several feet wide, passes upwardly over a feeding table 17 between the endless belt and the plate glass. As it passes over the glass it is subjected to light from a suitable source, such as a series of arc lights 18, during which exposure the printing operation takes place, after which it may be developed.

The pressure plate 15 has lugs 19thereon having sliding engagement with pins 20, the latter being secured in a fixed plate 21 forming one wall of an enclosure. This arrangement maintains the plate 15 parallel with the glass, thereby causing the sheet of sensitive material to be uniformly pressed against the glass. The side and end walls thereof are shown at 22 secured to the wall 21, and inside of the wall 22 is a flexible or extensible airtightv member 23 such as a sheet of rubber, bent back and forth to form, in effect, a bellows arrangement, one edge of said flexible member being secured to the stationary wall 21, suitably secured to the frame of the ma chine, and the other edge tothe plate 15, constituting the movable wall of the chamber. Fluid under pressure is admitted to the chamber through the pipe 24 and the pressure regulated in any convenient nanner and indicated by a gauge 25. Compressed air'is suitable for the purpose and may be so controlled as to produce any required pressure of the plate 15 against the sensitized paper and thus against the negatives or tracings which travel along with the paper between the latter and the plate glass.

With this arrangement the resulting prints are sharp and-uniform, and the printing is faster due to the direct light penetration through the flat glass, which does not deflect the light rays as much as a curved glass. Owing to this more ra id printingand correv spondingly decreased time of exposure, it is possible to use a greatly reduced glass area; in other words, a shorter piece of glass. The smaller glass not only reduces the initial manufacturing cost, but makes it possible commercially, to obtain more readily, a perfect plate of glass with a true, highly polished flat surface. Furthermore, the decreased glass area offers proportionately less resistance to the passage of the tracings, negatives and sensitizedpaper; also pressure can be more readily applied to a flat glass surface than to thesurface of curved glass.

Although the pressure means is more advantageously applied to .a flat piece of plate glass, it is possible also .to use it and retain some of the advantages enumerated in conjunction with a curved glass. Various other changes and modifications may be made without departing from the invention .as expressed in the appended claims.

What I claim is: 1

1v Photoprinting apparatus comprising sheet of transparent material, a source of light on one side thereof, meansfor drawing a sheet of sensitized paper continuously past the opposite side thereof, a chamber having a'ri-gid movable wall adjacent said sheet of sensitized paper and containing a fluid under pressure whereby said wall may press said moving paper against said transparent material, and means within said chamber for maintaining said wall parallel with said transparent material, 7

2. Photoprinting apparatus comprising a flat sheet of glass, an endless belt in contact therewith, means causing said belt to travel over said glass, a chamber having :a rigid yielding wall parallel with and inengagement with saidbelt to increase said contact and a source of fluid pressure in communication with said chamber to force said wall outwardlya I 3. Photoprinting apparatus comprising'a flat sheet of glass, an endless belt travelling in contact therewith, a chamber having a rigid yielding wallin engagement with said belt to increase said contact, said chamber having a rigid supporting wall, a flexible side wall connecting the same to said yielding wall and means for maintaining the latter parallel with said glass in its movements toward and away from said supporting wall.

4. Apparatus of the class described comprising a sheet of plate glass having a flat polished surface, a pair of rollers near opposite ends thereof, an endless belt passing over said rollers adjacent to said polished surface, a pressure'plate located between said rollers and engaging the side of the .belt opposite that engaged by said polished surface, a plurality of hollow bosses on said pressure plate, a stationary plate substantially parallel thereto, pins mounted in saidstationary plate and enterin said hollow bosses to per" mit said pressure plate to move toward and my name. I

HAROLD J. BRUNK.

111g completely around the same'to form a 

